1. Field of the Invention
The present invention relates to computer systems, and more specifically to a method and apparatus for writing servo-track information on a disk drive with non-overlapping read and write elements.
2. Description of Related Art
Information for electronic systems such as computer and data processing systems is typically stored on storage media such as magnetic disk drives. Recently, increased storage capacity in floppy and hard disk drives has been achieved by using higher track densities that are made possible by the use of voice-coil and other types of servo-positioners and technologies such as magneto-resistive head technology that allow narrower tracks to be read and written. While conventional low density disk drives achieved satisfactory head positioning with leadscrew and stepper motor mechanisms, the higher track densities currently being used make the mechanical error of such a motor mechanism so great as to become significant compared to the track-to-track spacing. Thus, high density drives require an embedded servo that can read servo-patterns from the disk and determine the position of the head.
Conventional servo-patterns (or servo-data tracks) generally take the form of short bursts of a constant frequency signal that are very precisely located. More specifically, it is critical that the head follow the center line of a data track during both reading and writing. Thus, servo-data is typically written on both sides of the data track so as to be offset from the center line of the data track. Further, the servo-data is generally dispersed around the data track by writing short bursts in each of the sixty or so sector header areas of the data track. Such data bursts can be used by the embedded servo mechanism to find the center line of the data track. This allows the head to follow the track center line around the disk even when the track is out of round (e.g., due to spindle wobble, disk slip, or thermal expansion). As the size of disk drives is reduced and track density is increased, the servo-data must be more accurately located on the disk.
FIGS. 1(a) and 1(b) show a conventional servo-data pattern on a disk. As shown, circular data tracks are broken into sectors 7 that each have a sector header area 7 followed by a data area 9. Each sector header area 8 includes sector header information 2 followed by a servo-data area that provides radial position information. The sector header information 2 includes a servo-identification (SID) field 4 and a grey code field 6 that must be precisely aligned from track to track to prevent destructive interference in the magnetic pattern. Such interference can reduce the amplitude of the signal and cause data errors.
During conventional drive manufacturing, the disk drive is typically mounted in a mastering station that is known as a servo-writer. The servo-writer has sensors that are positioned outside of the disk drive to locate the radial and circumferential position of at least one of the drive""s internal heads. Using information from the sensors, the servo-writer causes the head to write a pattern of magnetic information (i.e., servo-data) onto the disk. As explained above, the servo-pattern becomes the master reference used by the disk drive during normal operation to locate the tracks and sectors for data storage. When such a station is used to perform the servo-writing, manufacturing expenses increase because each disk drive must be mounted in the servo-writer. Additionally, the mechanical boundary conditions of the disk are altered because the external sensors must have access to the actuator and the disk spindle motor. Thus, mechanical clamping and disassembly of the drive may also be required.
One conventional servo-writing process is disclosed in U.S. Pat. No. 4,414,589. In the disclosed process, a servo-track following system is used to position a moving read/write head relative to a magnetic storage disk. A plurality of servo-data tracks are recorded in sectors of the disk to identify radial positions or data tracks. In particular, a clock track is written by writing a single pulse on a fixed clock track head, phase-lock looping to an intermediate clock track that is written by a moving head, and then phase-lock looping up to the final clock track that is written on the fixed clock track head.
Radial track density is then determined by moving a head to a limit stop and writing a reference track. Next, the head is displaced an amount sufficient to reduce the amplitude of the reference track by a predetermined percentage that is related to the ultimate average track density, and another reference track is written. The head is then again displaced from the second reference track to again reduce the amplitude of the reference track by a predetermined percentage. This is repeated until the disk is filled with reference tracks. If the final average track density is unsatisfactory, the percentage is adjusted and the process is repeated.
Another conventional servo-writing process is disclosed in U.S. Pat. No. 4,531,167. According to this process, a master clock track is first written on the disk by a separate head to serve as a timing reference for the entire servo-track writing operation. After writing the master clock track, xe2x80x9cevenxe2x80x9d servo-data bursts are written over the entire surface of the disk by first moving the arm to the outer crash stop and then radially moving the arm a distance that is less than a data track width for each revolution of the disk.
After reaching the inner diameter of the disk, the arm is once again moved to the outer crash stop and then radially moved for each revolution of the disk to write xe2x80x9coddxe2x80x9d servo-data bursts are written. After servo-writing is completed, the number of steps of the arm from the outer crash stop to the inner crash stop is compared with the desired number of tracks. If the number of steps is different from the desired number of tracks, a bias is introduced and the process is repeated so that the number of steps will equal the desired number of tracks.
Such conventional servo-writing procedures require the use of an external timing sensor in order to write the timing patterns that are used to determine the circumferential head position. Because external sensors are needed, the servo-writing must be performed in a clean room environment. Additionally, an external clock source and auxiliary clock heads are required to write the timing information. Further, in such procedures, an entire disk of information must be written to determine the track pitch to use to write the servo-pattern. This takes times and leads to increased manufacturing costs.
To overcome such problems, self-servo-writing timing generation processes have recently been developed. These processes allow accurately aligned servo-data tracks to be written sequentially at each servo data radius without using any mechanical, magnetic, or optical positioning systems. Further, the need for auxiliary clock heads to write a reference timing pattern on the disk is eliminated. While such self-servo-writing processes are sufficient when the servo-data tracks are to be written using overlapping read and write heads (i.e., where a track can be written and read without changing head position), disk drives with non-overlapping read and write elements are now being produced.
More specifically, as read and write element dimensions have been decreased to increase storage density, the widths over which reading and writing occur have decreased more rapidly than the distance between the read and write elements themselves. As a result, when using a head with such elements on a rotary actuator, the read element of the head can no longer overlap the area written by the write element of the head at all radial positions. When the known self-servo-writing processes are used for drives in which the read and write elements do not overlap, accurate circumferential alignment of the servo-data tracks cannot be maintained and there is a lack of stability against the growth of random errors in the pattern generation process.
In view of these drawbacks, it is an object of the present invention to remove the above-mentioned drawbacks and to provide a self-servo-writing process for use with non-overlapping read and write elements that produces servo-data tracks having accurate circumferential alignment.
Another object of the present invention is to provide a self-servo-writing process for use with non-overlapping read and write elements that has stability against the growth of random errors in the pattern generation process.
One embodiment of the present invention provides a method of writing a servo-pattern on a storage medium. According to the method, first timing marks are written at a first radial position of the storage medium, and the head is moved to a second radial position. Time intervals between selected pairs of the first timing marks are measured, and other timing marks are written at the second radial position of the storage medium. The measuring step is performed after the moving step. In a preferred method, the steps of moving, measuring, and writing other timing marks are repeated until the servo-pattern is written on an entire surface of the storage medium.
Another embodiment of the present invention provides a method for generating an initial aligned pattern of timing marks for self-servo-writing on a storage medium. According to the method, a first set of unaligned timing marks is written such that at some radial position of a read element more than one of the timing marks is detected. Relative locations of the unaligned timing marks are measured, and an aligned pattern is written by adjusting the time delay for writing based on the timing mark being read by the read element and a calculated position of that timing mark.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.